Comment: It’s time for a DC homecoming



Blane Judd chairs the IET’s built environment panel

While my article was protected because I was using the laptop, which just transferred to battery, the online Christmas shopping list my wife was busy working through was lost as the router and desktop machine just quit. Worse still, the Sky box did not record Andrew Marr, a serious catastrophe in our household.

Strange how these failures of technology always seem to be my fault (the burden of being an engineer I assume), but I was able to quickly point the finger at Mr Nikola Tesla. Conveniently he is not able to defend his position – and to be fair he had no knowledge of the impending development of semiconductor technology that uses direct current as its power source.

His most heinous of crimes was to extol the virtues of the now-near universal Alternating Current power supply, which reverses its flow some hundred times a second, which for a power hungry industrial revolution was exactly what was needed.

The trouble with DC

But back to a Sunday in the 21st century and all hell breaks loose as every electrical appliance takes the form of a useless ornament. I am not able to get the gas oven to ignite to start cooking breakfast: the gas solenoid valve refuses to open as there is no power. The boiler, a combi unit, refuses to supply heating and hot water for the same reason. Thank goodness for the gas lighter used for the log burner, I can boil some water in a pan on the gas hob and we can have a cup of tea.

I have already highlighted the consequence of the failed Sky box and associated television. None of the LED lighting will spark to life and it is a miserable grey day outside. To add insult to injury, a Yodel delivery person knocks at the door (the transformer for the bell is temporarily just a brick) to deliver a birthday present from my son, an Amazon Echo, so that can stay in the box.

It could have been so different

Now let us suspend reality for a moment and assume that Thomas Edison had won the war of the currents in the 1880s. How different would the day have been?

For a start the batteries in my under-stairs cupboard would have continued to supply the DC circuits in my home. Their efficiency would have been developed over years of innovation. The photovoltaic panels would be struggling a bit under the grey skies but still provide a trickle charge. The single point transformer rectifier connected to the AC distribution circuit in the street would have shut down (it still makes sense to transmit and distribute over long distances using AC).

All of my semiconductor devices would be happily drawing their power from the independent supply in my home. Mr Marr’s guests and newspaper review would be captured only to be deleted later, because we watched it live anyway, the TV and the Sky box having dispensed with its need for a transformer rectifier or switch mode power supply units.

The router would have continued to have functioned and the desktop machine would not have shut down: Christmas saved yet again! Incidentally, my electricity bills would be less than the total Christmas food shop, just clocked up by my wife.

The solenoid on the gas valves are not discriminatory and so gas would have flowed and been ignited by a spark ignitor that was grateful for any power source. The developments in DC brushless motors and perhaps halogen water heating, in domestic appliances, would mean the washing machine and dishwasher would be happily doing their thing. Even the alternative wholesome hot water device (which used to be called a kettle) can supply the necessary temperature water for my cup of tea.

There have been consequences

But it is not just the inconvenience that would have been saved. According to the Independent newspaper, sometime in 2014 the number of mobile devices exceeded the number of people on the planet. Each device coming with its own AC to DC charging device.

Add to that the billions of electrical products (US EPA) that contain rectifying power supplies and the millions that are sold each year an estimated consumption of 200bn kWh/year is not unreasonable (EPRI).

Consider the carbon emissions (circa 24m tons per year), wasted energy in heat (I2R losses) together with the embedded copper and aluminium in each device, eradication has a global benefit.

It’s time to look at DC for the home

If all of that were not enough to encourage different thinking about the utility of direct current in domestic and commercial environments, consider finally the number of people who were without a loved one this Christmas, due to the number fatalities over the years, through electric shock from high voltage supplies, which would have been unlikely with low voltage direct current systems in their home.  Low voltage plugs and sockets are not only safer but much more compact – what’s not to like?

Happy New Year.

Blane Judd chairs the Built Environment Policy Panel of the Institution of Engineering and Technology (IET)


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